The network would not broadcast a TV spot entitled "Rip, Burn, Respect" that promotes legal music downloading with Gateway hardware and software.
"We don't accept advocacy advertising and this particular ad fell under that umbrella," a CBS spokesman said.
The network and its parent, Viacom, have lobbied against music piracy in Washington, having helped bring Napster to its knees.
Just music jargon
The offending ad, meanwhile, has aired on most other networks. The spot is an innocuous tableau of hipsters spouting Internet music jargon. It was created by a company called Dogmatic and directed by a photographer named Gobi and Laurel Harris, owner of Dogmatic.
"It's kind of exciting," Ms. Harris said about the controversy surrounding her work.